glBegin(3G) OpenGL Reference glBegin(3G)
glBegin, glEnd - delimit the vertices of a primitive or a group of like
primitives
void glBegin( GLenum mode )
mode Specifies the primitive or primitives that will be created from
vertices presented between glBegin and the subsequent glEnd. Ten
symbolic constants are accepted: GL_POINTS, GL_LINES,
GL_LINE_STRIP, GL_LINE_LOOP, GL_TRIANGLES, GL_TRIANGLE_STRIP,
GL_TRIANGLE_FAN, GL_QUADS, GL_QUAD_STRIP, and GL_POLYGON.
void glEnd( void )
glBegin and glEnd delimit the vertices that define a primitive or a group
of like primitives. glBegin accepts a single argument that specifies in
which of ten ways the vertices are interpreted. Taking n as an integer
count starting at one, and N as the total number of vertices specified,
the interpretations are as follows:
GL_POINTS Treats each vertex as a single point. Vertex n
defines point n. N points are drawn.
GL_LINES Treats each pair of vertices as an independent
line segment. Vertices 2n-1 and 2n define line n.
N/2 lines are drawn.
GL_LINE_STRIP Draws a connected group of line segments from the
first vertex to the last. Vertices n and n + 1
define line n. N-1 lines are drawn.
GL_LINE_LOOP Draws a connected group of line segments from the
first vertex to the last, then back to the first.
Vertices n and n + 1 define line n. The last
line, however, is defined by vertices N and 1. N
lines are drawn.
GL_TRIANGLES Treats each triplet of vertices as an independent
triangle. Vertices 3n-2, 3n-1, and 3n define
triangle n. N/3 triangles are drawn.
GL_TRIANGLE_STRIP Draws a connected group of triangles. One
triangle is defined for each vertex presented
after the first two vertices. For odd n, vertices
n, n + 1, and n + 2 define triangle n. For even
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glBegin(3G) OpenGL Reference glBegin(3G)
n, vertices n + 1, n, and n + 2 define triangle n.
N-2 triangles are drawn.
GL_TRIANGLE_FAN Draws a connected group of triangles. One
triangle is defined for each vertex presented
after the first two vertices. Vertices 1, n + 1,
and n + 2 define triangle n. N-2 triangles are
drawn.
GL_QUADS Treats each group of four vertices as an
independent quadrilateral. Vertices 4n-3, 4n-2,
4n-1, and 4n define quadrilateral n. N/4
quadrilaterals are drawn.
GL_QUAD_STRIP Draws a connected group of quadrilaterals. One
quadrilateral is defined for each pair of vertices
presented after the first pair. Vertices 2n-1,
2n, 2n + 2, and 2n + 1 define quadrilateral n.
N/2-1 quadrilaterals are drawn. Note that the
order in which vertices are used to construct a
quadrilateral from strip data is different from
that used with independent data.
GL_POLYGON Draws a single, convex polygon. Vertices 1
through N define this polygon.
Only a subset of GL commands can be used between glBegin and glEnd. The
commands are glVertex, glColor, glIndex, glNormal, glTexCoord,
glEvalCoord, glEvalPoint, glArrayElement, glMaterial, and glEdgeFlag.
Also, it is acceptable to use glCallList or glCallLists to execute
display lists that include only the preceding commands. If any other GL
command is executed between glBegin and glEnd, the error flag is set and
the command is ignored.
Regardless of the value chosen for mode, there is no limit to the number
of vertices that can be defined between glBegin and glEnd. Lines,
triangles, quadrilaterals, and polygons that are incompletely specified
are not drawn. Incomplete specification results when either too few
vertices are provided to specify even a single primitive or when an
incorrect multiple of vertices is specified. The incomplete primitive is
ignored; the rest are drawn.
The minimum specification of vertices for each primitive is as follows:
1 for a point, 2 for a line, 3 for a triangle, 4 for a quadrilateral, and
3 for a polygon. Modes that require a certain multiple of vertices are
GL_LINES (2), GL_TRIANGLES (3), GL_QUADS (4), and GL_QUAD_STRIP (2).
GL_INVALID_ENUM is generated if mode is set to an unaccepted value.
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glBegin(3G) OpenGL Reference glBegin(3G)
GL_INVALID_OPERATION is generated if glBegin is executed between a
glBegin and the corresponding execution of glEnd.
GL_INVALID_OPERATION is generated if glEnd is executed without being
preceded by a glBegin.
GL_INVALID_OPERATION is generated if a command other than glVertex,
glColor, glIndex, glNormal, glTexCoord, glEvalCoord, glEvalPoint,
glArrayElement, glMaterial, glEdgeFlag, glCallList, or glCallLists is
executed between the execution of glBegin and the corresponding execution
glEnd.
Execution of glEnableClientState, glDisableClientState,
glEdgeFlagPointer, glTexCoordPointer, glColorPointer, glIndexPointer,
glNormalPointer, glVertexPointer, glInterleavedArrays, or glPixelStore is
not allowed after a call to glBegin and before the corresponding call to
glEnd, but an error may or may not be generated.
glArrayElement, glCallList, glCallLists, glColor, glEdgeFlag,
glEvalCoord, glEvalPoint, glIndex, glMaterial, glNormal, glTexCoord,
glVertex
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